1. Field of the Invention
The present invention relates particularly to a capacitor with high long-term reliability and its producing method among those used for various types of electronic devices, regeneration for a hybrid vehicle, storing power, and others.
2. Background Art
FIG. 13 is a partial cutaway perspective view illustrating the structure of an electric double layer capacitor as an example of a conventional capacitor. FIG. 14 is a sectional view of the substantial part of a capacitor element included in the capacitor shown in FIG. 13. The capacitor includes capacitor element 31, case 39, and sealing member 40.
Capacitor element 31 is formed of positive electrode 32 and negative electrode 33 wound with separator 34 placed therebetween. Positive electrode 32 and negative electrode 33 are structured by forming polarizable electrode layers 36 containing carbon on both sides of collector 35 made of aluminum foil. Positive electrode 32 and negative electrode 33 have leads 37, 38 connected thereto, respectively.
Capacitor element 31, after being impregnated with an electrolyte solution (not shown), is inserted into case 39. Case 39 made of metal is cylindrically shaped and has a bottom. Next, leads 37, 38 are inserted into holes provided in sealing member 40 made of rubber, respectively. In such a state, sealing member 40 is placed at the opening of case 39. After that, the outer circumference of the opening of case 39 is drawn inwardly, and the open end of case 39 is curled toward sealing member 40 to seal case 39. The electrolyte solution is prepared from mainly propylene carbonate (PC) used as the solvent with tetraethylammonium salt or the like as the solute.
However, when the above-described conventional capacitor is left in an open state between leads 37, 38 after being charged, the voltage gradually decreases due to a self-discharge phenomenon inherent in the capacitor. Such a voltage drop generally causes no problem at all. However, using the capacitor for starting an engine of a vehicle, for example, will cause a large trouble such as failing to start the engine due to the voltage drop.